Field
Aspects of the present disclosure generally relate to fabricating an armored cable having one or more optical fibers contained therein. More particularly, aspects of the present disclosure relate to reducing friction and static charge when inserting the one or more optical fibers in one or more guide tubes during fabrication of the armored cable.
Description of the Related Art
Downhole optical fiber cables are often manufactured using an outer armor for protection of one or more optical fibers contained therein. It is often desirable to have some amount of excess fiber length (EFL) in the armored cable, for example, to reduce strain on the optical fibers. EFL generally refers to an excess length of the fiber relative to the outer armor.
The outer armor may typically be formed by seam welding the outer armor over another (inner) tube that contains the optical fibers. The inner tube may protect the optical fiber from the extreme heat generated during the welding process. However, the use of an inner tube adds substantial cost to the armored cable.
In some cases, the optical fiber(s) may be put into an armor tube after the tube is manufactured by pushing fiber into the tube with the aid of gas or liquids. Unfortunately, this is a costly and time-consuming process and, in addition, it is difficult to achieve a desired amount of EFL.
For example, one or more optical fibers may be pushed into a metal tube when manufacturing a fiber in metal tube (FIMT), as described in U.S. Pat. No. 7,024,081 to Dowd et al., herein incorporated by reference in its entirety. During fabrication of a FIMT, the metal strip stock may be fed into the forming rollers which then pull the strip along as the strip is formed into a tube and welded at the seam. The tube may be welded somewhat larger in diameter than the finished tube size at this point. The optical fibers and gel material (if used) may be fed through guide tubes parallel to the strip stock and past the welding zone. The optical fibers are not pushed into the guide tubes; rather, the fibers get caught in the seam-welded metal tube by friction and are pulled at low tension from payoff spools through the guide tubes and into the metal tube. If used, gel will aid in pulling the fibers and can also have limited control of the overstuff, based on gel pumping volume. After welding, while still on the line, the assembly may be pulled through a sizing die to form the final FIMT diameter. A capstan may be located downstream of the die. The force involved in pulling the oversized tube through the die also stretches the tube, pulling extra fiber in from the fiber payoff spool. When the FIMT exits the capstan, the tension is reduced, and the FIMT has a small relax in length, yielding fiber overstuff. This method may be difficult to perform successfully with ¼″ heavy wall cable.
As an alternative, fiber overstuff may be added to the tube by running the tube through a series of rollers, which works the metal and effectively shrinks the length of the tube. This alternative method can be used for larger tubes, like ¼″, but is limited in the amount of overstuff that can be achieved and also entails extra processing.